.first-container {
    height: 100%;
    width: 100%;
    display: flex;
    flex-direction: column;
    background-color: #fff;
}

.header {
    height: 55%;
    width: 100%;
    padding: 0 !important;
    display: flex; /**/
    justify-content: center; /*水平居中*/
    align-items: Center; /*垂直居中*/
    background-color: black;
    overflow: hidden;
}

.second-container {
    flex: 1;
    margin-top: 20px;
    box-sizing: border-box;
    overflow: hidden;
}